1. Field of the Invention
The present invention relates to an oxetane compound, a process for producing the same, and an oxetane copolymer. More specifically, the present invention relates to an oxetane compound which has an excellent property in radical polymerization, cationic polymerization, compatibility and copolymerization-ability with other unsaturated monomers (vinyl monomers or the like); a process for producing such an oxetane compound effectively; and an oxetane copolymer containing a fluorine component as a copolymerization component.
2. Description of the Background
Epoxy resins have been widely used as a photocuring component in photocuring compositions since they are excellent in heat resistance, adhesion to various substrates and cationic polymerization.
However, reaction of a photocuring composition using a conventional epoxy resin is not easily controlled in the presence of an acid or alkali. The composition reacts even at room temperature. Problems that preservation stability and convenience are poor arise.
For this reason, suggestions as follows are made on: a photocuring component and a photocuring catalyst are physically divided in a photocuring composition using an epoxy resin so as to prepare a so-called two-liquid type adhesive. However, before use, the photocuring component and the photocuring catalyst must be homogeneously mixed. Thus, convenience thereof is poor and bad photocuring is caused because of insufficient mixing.
Thus, as cationic polymerizable resins instead of epoxy resins, oxetane compounds are suggested. For example, JP-A-6-16804, JP-A-7-53711, JP-A-7-62082, JP-A-9-31186, JP-A-7-173279 and JP-A-9-143259 disclose photocuring oxetane compositions containing as a main component an oxetane compound which does not contain ether bonds other than any oxetane group (active energy beam curing compositions).
Furthermore, JP-A-7-17958 discloses an oxetane compound represented by the following general formula (6); an ultraviolet ray curing composition comprising the oxetane compound and a cationic photopolymerization initiator; and a process for producing an oxetane compound, using a synthesis process by Pattison (Pattison, J. Am. Chem. Soc., 1958, 79). 
wherein T1 represents hydrogen, alkyl having 1 to 6 carbon atoms, fluorine, fluoroalkyl having 1 to 6 carbon atoms, ally, aryl, furyl or thienyl, T2 represents alkyl having 1 to 6 carbon, and T3 represents hydrogen or alkyl having 1 to 6 carbon atoms.
However, the oxetane compound represented by the general formula (6) has insufficient radical polymerization-ability. Thus, there arise problems that the oxetane compound has poor copolymerization-ability with other unsaturated monomers, in particular fluorinated monomers. According to the synthesis process by Pattison used to synthesize the oxetane compound represented by the general formula (6), it is impossible to synthesize any oxetane compound containing in the molecule thereof plural ether bonds other than any oxetane group.
Thus, the inventors of the present invention made investigations eagerly. As a result, the inventors have found that the above-mentioned problems can be solved by causing plural ether bonds other than any oxetane group to be contained in the molecule of an oxetane compound.
The inventors have found that plural ether bonds other than any oxetane group contained in the molecule could improve remarkably the radical polymerization-ability of unsaturated groups in the oxetane compound while the cationic polymerization-ability of the oxetane group is maintained.
The inventors have also found that by causing plural ether bonds other than any oxetane group to be contained in the molecule, the compatibility with other copolymerizable monomers and radical polymerization-ability are improved so that copolymers having uniform properties can be obtained.
Thus, an object of the present invention is to provide an oxetane compound excellent in radical polymerization-ability and cationic polymerization-ability and in copolymerization-ability; and an oxetane copolymer obtained from such an oxetane compound.
Another object of the present invention is to provide a process for producing an oxetane compound effectively.
The present invention is an oxetane compound which contains in the molecule thereof plural ether bonds other than any oxetane group and is represented by the general formula (1): 
wherein substituent R1 is hydrogen, alkyl, fluorine, fluoroalkyl, ally, aryl, furyl or thienyl; substituents R2, R3 and R4 each independently is hydrogen or alkyl having 1 to 6 carbon atoms; and m and n each is an integer of 1 to 10 (excluding a compound where in all of substituents R2, R3 and R4 are not hydrogen).
The oxetane compound having the above-mentioned structure is excellent in radical polymerization-ability and cationic polymerization-ability and in compatibility with other copolymerizable monomers.
Another aspect of the present invention is an oxetane copolymer obtained by radical polymerizing an oxetane compound represented by the general formula (1) (including a compound wherein all of the substituents R2, R3 and R4 are hydrogen), its number average molecular weight converted to polystyrene, which is measured by GPC, being in the range of 1,000 to 1,000,000.
For example, the oxetane copolymer is represented by the general formula (2): 
wherein substituent R1 is hydrogen, alkyl, fluorine, fluoroalkyl, ally, aryl, furyl or thienyl; substituents R2, R3 and R4 each independently is hydrogen or alkyl having 1 to 6 carbon atoms; R5 is hydrogen, fluorine or chlorine; R6 is hydrogen, fluorine, fluoroalkyl, alkoxy or fluorinated alkoxy; m and n each is an integer of 1 to 10; a and b each is in the range of 0.1 to 99.9% by mole(a+b=100 mol %).
Note that both ends of the main chain of the general formula (2)(both ends are not described in the general formula (2)) are hydrogen, groups composed of a part of a radical polymerization initiator, or the like.
The oxetane copolymer having the above-mentioned structure is excellent in compatibility with a fluorine compound as a copolymerization component and in water repellence and transparency, and has a low water absorption property. Also, such oxetane copolymer has a good photocuring property.
A further aspect of the present invention is a process for producing an oxetane compound represented by the general formula (1), characterized by reacting an oxetane alcohol compound represented by the following general formula (4) with a halogenated vinyl ether compound represented by the following general formula (5) in the presence of a phase transfer catalyst: 
wherein substituent R1 and repetition number m are the same in the general formula (1), 
wherein substituents R2, R3 and R4 and repetition number n each is the same in the general formula (1), and X is a halogen atom.
By such process for producing an oxetane compound, it is possible to produce effectively an oxetane compound excellent in both of radical polymerization-ability and cationic polymerization-ability and in compatibility with other copolymerizable monomers.